Given the global trade in goods that has developed which increasingly includes goods that require cooling during transport, and given the increasing requirements of people for comfort, the need for cooling systems is continuously increasing and hence in particular the need for compressor units and compressors that supply the cold for the aforementioned cooling systems. In times in which energy resources are expensive and not least because minimal energy consumption is desirable due to environmental policy considerations, efforts are underway to design refrigerant compressors as small as possible, as simple as possible, and weighing as little as possible. Furthermore, a goal is to design corresponding compressors for use with environmentally-friendly refrigerants such as CO2 as the refrigerant (refrigerant R744) in order to thereby restrict use of fluorocarbon-containing refrigerants.
A radial piston compressor which is designed for CO2 as the refrigerant is for example known from EP 1 552 291 B1 which discloses a reciprocating engine in the form of a radial piston compressor with a compressor unit having annular, radially aligned piston cylinder units arranged next to each other, and with an eccentric shaft. The eccentric shaft extends through a housing body of a machine housing which encloses the cylinders, and the eccentric thereof controls the outward stroke of the pistons. The inward stroke of the pistons is controlled or respectively instigated by a common control ring engaging in the pistons. The control ring is engaged in a lateral recess in each piston, running in the direction of a secant, and being adapted to a cross-sectional shape of the control ring, and bordering a floor wall of the piston, wherein the control ring is in controlling sliding contact with this floor wall by means of an inner control surface.
This design of a radial piston compressor according to EP 1 553 291 B1 is relatively complicated. Furthermore, the polygonal (hexagonal) return ring according to EP 1 553 291 B1 for the return movement of the pistons slides within the piston grooves perpendicular to the direction of traction. In addition to limiting the available or respectively useful return forces, this also results in a tendency of the ring to tilt. The above-described construction also constitutes an arrangement that provides a “one-sided” engagement by the return ring in the piston grooves and hence one-sided material stresses. In particular with multistage compressors in which high return forces are required, a return mechanism is also required that can withstand the corresponding forces.
Based on the above-discussed preceding art, it is therefore the object of the present invention to present a compressor unit of a compressor for compressing refrigerant which, in comparison to the compressor units according to the preceding art, is universally useable, relatively easy to design and hence also economical to manufacture. Furthermore, it is the object of the present invention to present a corresponding compressor.